1. Field of the Invention
The present invention relates to an image formation apparatus for optimizing image formation conditions in accordance with an original density and for automatically controlling the image density.
2. Description of the Prior Art
In a conventional image formation apparatus such as a copying machine, an original density is detected, and image formation conditions such as a charging condition, an exposure condition or a developing condition are controlled in accordance with the detection result obtained, thereby automatically controlling the image density.
Such automatic control of the image density can be performed by prescanning for light exposure amount correction after the pre-rotation of the photosensitive drum and correcting the light exposure amount in accordance with the result obtained by prescanning. However, according to this method, the photosensitive drum is first pre-rotated so as to render the surface thereof electrostatically uniform for standardization of the image formation conditions, and then prescanning for light exposure amount correction is performed. Therefore, due to the time for drum pre-rotation and light exposure amount correction, the copying operation for the first copy is delayed. Another method may be adopted to perform automatic control of the image density. According to this method, after the surface potential of the photosensitive drum has been adjusted to an optimum value, prescanning is performed to determine the amount of light illumination. The amount of illumination light determined in this manner is added to the amount of light obtained by standardization of the image formation conditions by control of the surface potential of the photosensitive drum. Then, the light exposure amount is thus controlled in accordance with the obtained sum. However, in this latter method, although the precision of the light exposure amount control is good, the copying operation for the first copy is again delayed.